A recent study has reported that cell phones could affect your brain activity in the part of the brain closest to the antenna. The study was meant to examine how the brain reacts to electromagnetic fields caused by wireless phone signals. Researchers found that your brain is affected by electromagnetic radiation in the region closest to the cellphone antenna when using the mobile phone.
Quoted from Yahoo! News,

While there was no overall change in brain metabolism, they found a 7 percent increase in brain metabolism in the region closest to the cellphone antenna when the phone was on.

Experts said the results were intriguing, but urged that they be interpreted with caution.

Some studies have linked cellphone exposure to an increased risk of brain cancers, but a large study by the WHO was inconclusive. When asked about the possibility of cancer, Dr. Nora Volkow of the National Institutes of Health says, “This study does not in any way indicate that. What the study does is to show the human brain is sensitive to electromagnetic radiation from cellphone exposures.”